Viruses are packets of infectious nucleic acid surrounded by protective coats which lack metabolic energy due to the absence of independent metabolism, and are incapable of growth by protein synthesis or reproduction apart from living cells. They have a prokaryotic genetic apparatus and usually contain either DNA or RNA, but not both and are usually covered by a protein shell or capsid which protects the nucleic acid.
The influenza or Orthomyxoviridae viruses cause the common influenza and influenza-like infections in humans and other mammals. These viruses contain negative single-stranded RNA as the genetic material and usually in eight segments. Included are influenza types A, B, and C as well as avian flu virus (H5N1).
The influenza virus infects the respiratory tracts of millions of people every year and is the cause of about 20,000 deaths annually in the US. The remarkable success of the influenza virus is due to genus Orthomyxoviridae's ability to undergo genetic reassortment to produce antigenic shift among its three types (species), A, B, and C, and within substrains. The genome of the Orthomyxoviruses is typified by eight segments of single-strand negative-sense RNA protected within a nucleocapsid structure. Each of the eight segments of the single-stranded negative-sense RNA codes for a particular viral protein: virion surface glycoproteins, hemagglutinin and neuraminidase for attachment process to the host cell surface receptor; matrix 1 and matrix 2 proteins for ion channel; PA, PB1, and PB2 for transcriptase and replicase enzymes for transcription and replication of viral genome; nucleocapsid, NP protein, for protection of all the viral genome segments from degradation by host RNase (FIG. 1). This nucleocapsid gene has a highly conserved region, and therefore, holds promise as a target against which an effective antiviral strategy can be developed.
RNA interference (RNAi) is a recently discovered and developed antiviral strategy in which gene silencing is effected by homologous short (21-23 bp) dsRNA fragments known as short interfering or siRNA. When a long dsRNA is introduced into a cell line, the cellular enzyme called Dicer will cleave it into short interfering RNA (siRNA) molecules. This short interfering RNA molecule is now called the guided RNA. The guided RNA will guide the RNA-Induced-Silencing-Complex (RISC) to the homologous target mRNA. Once it forms a hybrid structure to the homologous mRNA, the RISC will cleave the mRNA. As a result, protein that is encoded by the mRNA will no longer be produced and this will cause the silencing of the gene.
A recently published patent application, United States Patent Application Publication No. US 2004/0242518 A1 to Chen et al., published Dec. 2, 2004, discloses a siRNA (FIG. 21A, NP 1496) which partially overlaps the siRNA of this invention and cleaves at a different target nucleotide.